Rocky Mountain Oyster Day Date in the current year: October 5, 2026

Rocky Mountain oysters, also known as mountain oysters or prairie oysters in Canada, are an appetizer made from bull’s testicles. To prepare them, the testicles are skinned and coated in a mixture of flour, pepper, and salt. They are sometimes pounded flat before being deep-fried.

The exact origins of the dish are unclear. It was supposedly invented by 19th-century Colorado cowboys, but this is more of a culinary legend than an established fact. The consumption of animal testicles has long been widespread in many cultures and serves a practical purpose rather than a culinary one.

Castration is a common practice in animal husbandry for a number of reasons, and when calves are castrated, cattle farmers are left with a large quantity of testicles, which they may as well eat. While it is highly probable that 19th-century Colorado cowboys cooked deep-fried bull testicles, there is no proof that they invented the dish.

The first written mentions of the expressions “mountain oysters” and, more specifically, “Rocky Mountain oysters”, date back to the 1880s. However, the dish was not considered a regional Colorado specialty back then. Local bar and restaurant owners started to serve Rocky Mountain oysters and promote them as a regional dish around the mid-20th century. They are also often served at fairs and festivals. It’s a somewhat common prank to offer Rocky Mountain oysters to people who are unaware of what the dish is really made of.

Although Rocky Mountain oysters are promoted as a Colorado specialty, this dish is also popular in other states, including Idaho, Illinois, Michigan, Montana, Nevada, and Ohio. Several cities and towns in the region hold annual testicle festivals, some of which feature Rocky Mountain oysters alongside other dishes made from cattle testicles.

Some towns host events dedicated specifically to Rocky Mountain oysters. For example, Virginia City, Nevada, hosts an annual Rocky Mountain Oyster Fry in March as part of the Saint Patrick’s Day celebrations. Eagle, Idaho, claims to host the world’s largest Rocky Mountain oyster feed during its annual community festival, Eagle Fun Days, held in the summer.

Unlike many food-related holidays with obscure origins, Rocky Mountain Oyster Day has a clearly documented history. Created in 2017 by food writer Allyson Reedy, it was born out of her frustration that there were too many food holidays and none of them were linked to Colorado. She eventually decided that Rocky Mountain oysters deserved their own celebration and reached out to John-Bryan Hopkins, the man behind the Foodimentary calendar of food-related holidays.

Reedy pitched the idea, and Hopkins added Rocky Mountain Oyster Day as a new regional holiday on October 5. She also tried to obtain an official state proclamation, but was unsuccessful. Colorado restaurants and bars quickly adopted Rocky Mountain Oyster Day, offering various promotions for the occasion.